Do our trademarks conflict?

A Kuro5hin member named Water claims my software's trademarked logo
infringes another programs trademark. While both programs have the GNU
General Public License, they are both commercial products of private
companies. I would take any threat to my livelihood seriously, as I
imagine they would too:

I don't think there is actually a conflict, but it's easy to understand
why this fellow thought so.

To head off such a costly dispute, I'm seeking expert advice. If there
is any doubt whatsoever, I will of course consult an attorney. But the
best advice I can get at four in the morning is from debian-legal.

To put a stop to any speculation, I'll be writing up a page about it
based on my arguments below, but corrected any comments you may have. I
will link to it from the legal notices I have on each page of my site.

Before you read further, please look at our two logos. First
impressions in the public mind count significantly when the trademark
courts consider a dispute, as I will explain:

It's because I expect my digital music software to be popular with users
who don't understand Free Software. Thus I expect knock-off websites to
appear with downloads of knockoff software also called "Ogg Frog", but
that violate the GPL or the Creative Commons licenses of some of my
website's pages.

This happened to the peer-to-peer application eMule. eMule.org is a
cleverly-similar knock-off site that requires registration before one
can download the software. I'm not clear whether this actually violates
the GPL, but I imagine it would if registration were required to
download the source:

That's enough all by itself to convince me I'm right to use trademarks.
It's established that one can trademark Free Software; "Linux" is a
trademark in many countries, and "AbiWord" may only be applied to
verbatim copies of the word processor as distributed by AbiSource.
Derivative works are allowed to be called "AbiWord Personal":

I intend to do the same: the source I'll distribute will include a
different logo and Ogg Frog's name in the executable will be changed. I
assert this doesn't infringe the licenses of my GPL dependencies because
the text and graphics won't be linked, the act which brings the GPL to
bear on copies.

Why don't I infringe their trademark?
1. The Azureus frog logo is not actually a trademark.

2. Even if it were, my logo is not "confusingly similar" to theirs,
which I understand is what constitutes infringement.

3. The law allows trademarks to be identical provided that the
businesses or products are different enough, or separated
geographically. Thus the Canadian high court recently ruled that a
business may be called "McDonalds" if it doesn't sell fast food. Our
two programs are vastly different from each other.

4. Aelitis.com, the holder of the Azureus trademark, has not taken any
action to stop infringing use of the frog logo. Thus the legal
principle of estoppel would enable me to quash their trademark in court
if it ever came to that. I'm confident it won't.

Now in more detail:
1. Not a Trademark.

Extended Google searching was only able to find one page that mentioned
the Azureus frog in connection with a trademark, but it actually says:

"Belongs to" is not the same thing as "is a trademark of"; it's not
actually clear just what they're claiming. Their requirement that one
obtain permission before reproducing the logo, with the exception of
Fair Use, indicates that it is protected by copyright rather than
trademark.

Further, trademark law allows anyone to reproduce a trademark, provided
it is done verbatim and not in a way that casts doubt on its ownership.
I don't think it's even required to acknowledge the trademark's owner.
One just can't claim it as one's own.

That page may be in error, but I was also unable to find any claim to a
frog logo trademark on http://www.aelitis.com/

2. Not confusingly similar.

A an employee of a firm that provides expert testimony in trademark
disputes told me that confusing similarity was established by public
surveys where one is asked who the disputed trademark belongs to. They
carefully adjusted their questionairre iteratively to achieve results
for their clients.

Thus a St. Louis engineering firm had to change the gold color with
which they depicted the St. Louis arch in their logo. McDonalds
asserted it infringed on its famed golden arches, despite having only
one of them.

The only real similarity between their product and mine is that both are
GNU GPL software packages. Otherwise they are different enough that an
identical logo wouldn't be infringing.

Ogg Frog is a digital music application. Eventually it will play,
encode, tag, and rip music and burn music and data CDs. Azureus is a
BitTorrent client. One could argue that Azureus a music application
because its users download MP3s, but that would be quite a stretch.

While both can copy music, mine only copies music already in the user's
possession, while theirs downloads it from the Internet.

4. I can quash their trademark in court.

Before you protest that a Free Software advocate would never do such a
thing, I assure you I am certain it would never come to that. At worst,
all I would have to do is ask an attorney to explain how I could, and
they'd back down. I'll be posting all this on my site to make sure it
never even goes that far.

While a trademark on the logo could be claimed elsewhere than on the
web, such as the source code or About Box, searching at Google found
lots of pages where the frog was depicted without any acknowledgement of
its owner or that its a trademark. It's quite likely that some are
infringing uses, yet I don't see evidence that action was taken against
anyone.

That combined with the lack of any trademark notice on aelitis.com's own
website leads me to believe that the legal principle of estoppel would
allow me to quash their trademark.

Trademarks can be lost if you don't protect them, unlike patents and
copyrights, because the courts assume you tacitly gave permission for
their use in ways that would otherwise be infringing. Thus a small
clothing store called Saks 41st Avenue was forced by New York's Saks 5th
Avenue to change its name; Saks' attorneys told the local newspaper that
they were forced to do demand it or they would lose their valuable
trademark.

That's why I place the following notice on every one of my pages:
Ogg Frog, Rippit, Rippit the Ogg Frog, the Frog logo and the
Circle Flowers logo are trademarks of Michael D. Crawford.
All other trademarks are the property of their respective owners.

However, my logo doesn't include a "TM". I'm not certain it's actually
required, as long as I have the above notice on the same page. (The
fact that multitudes of otherwise lovely images have to be besmirched
with TMs and (R)s is, IMHO, a fault in our legal system right up there
with software patents and the DMCA: they are an Offense Against Art.)

Well, that about beats the subject to death. I'm grateful for any
advice you can give me.

After this is all settled, I'm going to separately ask your opinion as
to whether trademark text and graphics infringe the licenses of my
software's GPL dependencies. I don't think they do, but I could see why
one might think so.